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For further information, see CMDT Part 13-31: Hairy Cell Leukemia
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Essentials of Diagnosis
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Pancytopenia
Splenomegaly, often massive
"Hairy" cells present on blood smear and especially in bone marrow biopsy
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General Considerations
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Characteristically presents in middle-aged men
Median age at presentation is 55 years
Striking 5:1 male predominance
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Gradual onset of fatigue
Symptoms related to markedly enlarged spleen
Splenomegaly is almost invariably present and may be massive
Increased susceptibility to infection
Hepatomegaly in 50% of cases
Lymphadenopathy uncommon
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Differential Diagnosis
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Myelofibrosis
Chronic lymphocytic leukemia
Waldenström macroglobulinemia
Non-Hodgkin lymphoma
Aplastic anemia
Other cause of bone marrow infiltration, eg, metastatic cancer, infection
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Complete blood count
Peripheral blood smear: "hairy cells," with numerous characteristic cytoplasmic projections, may be present in small numbers
Hairy cells coexpress CD11c, CD20, CD22, CD25, CD103, and CD123 on immunophenotyping
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Diagnostic Procedures
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Bone marrow aspirate: often inaspirable (dry tap)
Bone marrow biopsy establishes diagnosis made by characteristic morphology
Pathologic examination of spleen shows marked infiltration of red pulp with hairy cells (in contrast to usual predilection of lymphomas to involve white pulp)
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Single course of pentostatin or cladribine
Treatment of choice
Median duration of response is over 8 years and patients who relapse a year or more from their initial therapy can be treated again with one of these agents
Treatment is associated with infectious complications and patients should be closely monitored
Rituximab can be used in the relapsed setting either as a single agent or in combination with a nucleoside analog
Vemurafenib, BRAF inhibitor
Exhibits ~100% overall response rate in patients with refractory/relapsed hairy cell leukemia, with 35–40% complete remissions
Median relapse-free survival is ~19 months in patients who achieved complete remission and 6 months in those who obtained a partial response
Moxetumomab pasudotox
A recombinant CD22-targeting immunotoxin approved for patients with refractory disease
Has shown a durable complete response rate of 31% in the pivotal trial
However, it can be associated with capillary leak and hemolytic-uremic syndrome attributable to the diphtheria toxin moiety
See Table 39–3
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